Copolyester adhesives

ABSTRACT

Copolyester adhesives are disclosed which are derived from at least 40 mol percent terephthalic acid, up to about 60 mol percent of another dicarboxylic acid selected from isophthalic, succinic, adipic, and glutaric, and a blend of 1,6-hexanediol and diethylene glycol.These copolyesters are useful as adhesives, and especially as fusible interlining adhesives.

This is a division of application Ser. No. 81,232 filed Oct. 2, 1979,now U.S. Pat. No. 4,252,940.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to certain copolyesters which have been found tobe useful as adhesives, especially fabric interlining adhesives.

2. Description of Prior Art

A fusible interlining is a material such as fabric which has been coatedon one side with a discontinuous pattern of fusible adhesive. When theinterlining is bonded to a face fabric in a garment, it provides bodyand shape to the garment without impairing the ability of the fabric tobreathe. Fusible interlinings are used, for example, in the manufactureof men's and women's suits, in shirt collars and cuffs, and in thewaistbands of trousers. In the manufacture of suits, polycarbonatebasting threads are frequently used to temporarily hold the parts of thesuit in place. After the suit is completed, a solvent such asperchloroethylene or trichloroethylene is used to embrittle thepolycarbonate thread so that it may be brushed from the fabric.

Certain polyesters are useful for fusible interlining applications.However, these polymers also tend to have certain disadvantages. Forexample, one polyester of interest is the copolyester of terephthalicacid, adipic acid, ethylene glycol and 1,4-butanediol as described inU.S. Pat. No. 3,699,921. Such polyesters tend to block in pellet formand Cab-O-Sil fumed silica, a product of Cabot Corporation, must beadded in significant amounts to make it possible to grind this polymerinto powder. Excessive amounts of Cab-O-Sil in the powder, however,prevent good coatability and good fusion of the powders on the fusibleinterlining fabric when applied with powder point applicators.

The use of polyesters with a melting point of 160° to 220° C. which arecomposed of terephthalic acid plus, in some cases, isophthalic acid andone or more glycols having 2 to 10 carbon atoms is disclosed in U.S.Pat. No. 3,853,665. Ethylene glycol, propylene glycol, butylene glycol,pentanediols or hexanediols are proposed as the glycols. As glycolmixtures, those mixtures are used which contain ethylene glycol,examples being ethylene glycol plus 1,6 hexanediol or ethylene glycolplus 1,4 butanediol. Such copolyesters have the disadvantages in thatthey have relatively high melting points. They are therefore usable toonly a limited extent as coating substances to be applied in the moltenstate or as fusion adhesives for heat-sensitive materials.

Copolyesters generally have lower melting points than homopolyesters.For example, the melting point of a polyester of terephthalic acid andethylene glycol is around 260° C. A polyester consisting of 90 mole % ofterephthalic acid and 10 mole % of isophthalic acid in which ethyleneglycol has been used as the diol component, has a melting point of 236°C. When the molar ratio of terephthalic acid to isophthalic acid is80:20, a copolyester is obtained which has a melting point of 210° C.When the ratio of terephthalic acid to isophthalic acid is 70:30 themelting point drops to 185° C.

Conditions are similar when ethylene glycol is replaced by 1,4butanediol. A polybutylene terephthalate comparable to polyethyleneterephthalate as a melting point of 225° C.

In German "Offenelegunggaschrift" No. 1,920,432 there is disclosed adry-cleaning fluid resistant polyester fusion adhesive prepared from (1)terephthalic acid and ethylene glycol, (2) adipic acid and 1,4butanediol. The molar ratio of terephthalic acid to adipic acid rangesfrom a predominance of terephthalic acid to a predominance of adipicacid, and the molar ratio of ethylene glycol to 1,4 butanediol rangesfrom a predominance of ethylene glycol to a predominance of 1,4butanediol. Such polyesters are used for bonding textiles. Thecopolyesters prepared in accordance with the example has a softeningpoint of 135° C. This softening point, however, is still too high formany heat-sensitive materials which are to be laminated or are to beprovided with a melted or sintered coating such as artificial leather,natural leather. If the molar ratios of the individual components ofthese copolyesters are varied, it is possible to arrive at a copolyesterhaving a softening point of 110° C. (terephthalic acid:adipic and molarratio 60:40 ethylene glycol:1,4 butanediol ratio 60:40. The degree ofcrystallization of this copolyester however, is already so low that itis not suitable for a fusion adhesive. Disadvantates reside in both thesurface stickiness of the coated substrate and the stickiness of thecopolyesters which is considerable even at room temperature.Copolyesters of this type are not suitable for the preparation ofcoating substances in powder form or adhesives in powder form such asrequired, for example, in the textile field.

It is well known in the art that the crystallinity of a polyester is oneparameter which may be used to determine solent resistance, i.e., themore amorphous (less crystalline), the more susceptible to dry-cleaningsolvents the polyester will be. It is also known that the inherentproperty of glass transistion temperature is also a parameter by whichthe temperature at which a polyester, evan an amorphous polyester, willbe effected by a solvent.

It is also known that modification of a homopolyester bycopolymerization with other acid or glycol moieties or combinations ofglycol and acid moieties to form copolymers or terpolymers drasticallyreduces or eliminates crystallinity. The crystallinity of copolyestersis also dependent on the particular comonomers from which thecopolyester is synthesized. For example, a polyester of terephthalicacid and 1,4 butanediol (even number of carbon atoms 4) will crystallizemore readily than a polyester prepared from terephthalic acid and either1,3 propanediol (odd number carbon atoms) or 1,5 pentanediol (odd numberof carbon atoms). The crystallization phenomenon of copolyesters,especially those that are low melting, below 150° C., is unpredictable.

Amorphous polyesters cannot be used as fusion adhesives in whichresistance to dry-cleaning and high set-up speed are required. In likemanner, those polyesters are undesirable which have too littlecrystallinity, because they solidify too slowly and consequently do notlose their surface stickiness for days or in many cases even weeks.

Since the requirements of crystallinity, set-up time, melting point andresistance to dry-cleaning are so numerous and are so dependent on somany interrelated and unrelated inherent monomer and polymer propertiesit is impossible to precisely design or produce useful copolyesters forthese applications.

Other low melting adhesives that we are aware of are those disclosed inU.S. Pat. Nos. 4,094,721 and 3,948,859.

SUMMARY OF THE INVENTION

In accordance with this invention, copolyesters suitable for use inapplications where low melting adhesives are required and especially infabric adhesive application, are provided. The copolyesters are preparedby copolymerizing the following:

(a) at least 40 mol percent terephthalic acid (TPA)

(b) up to 60 mol percent of another dicarboxylic acid selected fromisophthalic , succinic, adipic and glutaric

(c) about 10 to about 90 mol percent 1,6 hexanediol, and

(d) about 90 to about 10 mol percent diethylene glycol (DEG).

Besides having good adhesive properties, these copolyesters are lowmelting to provide resistance against scorching these copolyesterssintering, are resistant to dry-cleaning solvents, have goodgrindability, etc.

DESCRIPTION OF THE INVENTION

The copolyesters provided by the present invention are especially usefulas a fabric or textile adhesive. They are prepared by the condensationpolymerization of an acid moiety and a glycol moiety at least 40 molpercent of the acid moiety being a terephthalic acid moiety, and up to60 mol percent of another dicarboxylic acid moiety selected frommoieties of isophthalic, succinic, adipic and glutaric, the glycolmoieties being 10-90 mol percent 1,6-hexanediol moiety and 90-10 molpercent diethylene glycol moiety. Preferably, the mole percentages areabout as follows: terephthalic acid, 75 to 85; other dicarboxylic acid,25 to 15; 1,6-hexanediol, 75 to 85 and diethylene glycol, 25 to 15. Thecopolyesters should have an I.V. of about 0.4-1.2, a crystalline meltingpoint of about 40°-130° C., preferably about 80°-115° C., and a glasstransition temperature (Tg) of about -10° to about 30° C. The degree ofcrystallinity, measured by heat of fusion, ΔH_(f), should be greaterthan about 1.0 calorie per gram, preferably greater than about 3.0calories per gram. The practical upper limit of ΔH_(f) is about 10calories per gram. Also, the crystallization half time should be lessthan about 10 minutes at the maximum crystallization temperature.

The dicarboxylic acids and glycols specified for the copolyester arecommercially available or they may be prepared by well known procedures.The mol percentages specified are on the basis of 100 mol percentdicarboxylic acid and 100 mol percent glycol. The copolyesters areprepared by reacting the acid or acids with the two glycols in aconventional manner well known in the art.

The crystalline melting point, ΔH_(f), and T_(g) referred to above maybe measured by a Differential Scanning Calorimeter.

Ester forming derivatives of the acids referred to herein can beemployed, if desired, to prepare the copolyesters of this invention.Examples of such ester forming derivatives are the acids, anhydrides,esters and ester chlorides of such acids. For example, dimethylterephthalate may be employed in place of terephthalic acid; dimethyladipate can be used in place of adipic acid.

These copolyesters are readily put into powder form using conventionalgrinding techniques, preferably by cryogenic grinding. The powders arenonblocking and can be readily applied to fusible interlining fabricsfrom powder point applicators, from random sprinkling equipment, or inthe form of a paste. The particles are finely divided, i.e., from about1 micron to about 500 microns. In the application of powders from powderpoint applicators, it is desirable to have powders with a particle sizerange of 50-200 microns (270-70 mesh). For random sprinkling applicationon tightly woven or nonwoven fabrics, particle size of 150-300 microns(100-50 mesh) is desirable. For random sprinkling on open-weaver fabricssuch as cheap rayon/cotton blends, powders with 300-500 micron size(50-35 mesh) are required. For application of powder in paste form, itis necessary to have very fine powders. For example, in paste form,powder size should be 1-80 micron (less than 200 U.S. mesh). Thecopolyesters may also be used in strip or powder form.

The hot melt adhesives according to this invention are especiallydesirable because of their good grindability, i.e., ability to be groundinto a finely divided, free-flowing powdery form by conventionalgrinding techniques, and their resistance to blocking or caking duringstorage.

The "heat of fusion," ΔH_(f), of polymers is the amount of heat evolvedwhen crystallizable polymers are melted. ΔH_(f) values are readilyobtained using Differential Scanning Calorimeters (Perkin-Elmer). Forexample, one method for determining ΔH_(f) is described in Journal ofApplied Polymer Science, 20 1209 (1976). Measurement of ΔH_(f) is alsodescribed in duPont Thermal Analysis Bulletin No. 900-8 (1965).Qualitatively, it is possible to compare the degree of crystallinity ofpolymers by comparing their ΔH_(f) values.

One of the commonly used parameters for describing the crystallizationrate of a polymer is the crystallization half-time, t_(1/2). Thecrystallization half-time is simply the time at which thecrystallization of the originally amorphous sample is half completedaccording to the method used to monitor crystallinity and may bedetermined in conventional manners. The half-time is strongly dependenton the crystallization temperature.

One way of determining the isothermal crystallization of a polymer is anapproximation described by the Avrami equation ##EQU1## where X_(o) isthe limiting value of the crystallinity, is a characteristic timedetermined by the polymer and the crystallization temperature, and n isthe so-called Avrami exponent, generally in the range 2.0 to 3.5. Thereduced crystallization half-time, (t/τ)_(1/2), is obtained by solving##EQU2## The DSC response obtained would be described by differentiatingequation (1) with respect to time to get ##EQU3## This function has amaximum for all n>1. Differentiating equation 4 with respect to time,setting the derivative equal to zero and solvent for t/τ, one finds themaximum of dX/dt, which is the peak of the DSC curve, to be located at##EQU4## the ratio t_(p) /t_(1/2) is between 0.85 and 1.04 for n≧2. Thecurve of t_(p) vs. crystallization temperature is a sufficientapproximation of the curve t_(1/2) vs. crystallization temperature.

When copolyesters prepared as described above are employed as meltadhesives to laminate various fabric systems, metal strips and the like,excellent bonds result. These bonds are found to be highly resistant tothe action of dry cleaning solvents such as perchloroethylene. Thestrength of the bonds is determined by the so-called "Peel Test" basedon a modification of the ASTM "T-Peel Test" set forth on pages 63 and 64of the 1964 edition of the BOOK OF ASTM STANDARDS, published by theAmerican Society for Testing Materials, and more specifically identifiedas Test Number D-1876-61-T.

One method for determining the grindability of polymer samples is tocryogenically grind 10 g. of polymer pellets for 1 minute in thepresence of liquid nitrogen in a Micromill marketed by Chemical RubberCompany. The powder obtained is dried and seived through a 70 meshscreen. The grindability of a sample is defined as the percentage ofpowder which will pass through the 70 mesh screen.

If desired, dyes or dye receptive agents, color stabilizers and variousother adjuvants may be added to the copolyester adhesives to meetcertain specific end use requirements. Such additives would normally beadded as such to the polymerization mixture in which the copolyester isproduced.

As used herein, the inherent viscosity (I.V.) is measured at 25° C.using 0.50 gram of copolyester per 100 ml. of a solvent consisting of 60percent by weight phenol and 40 percent by weight tetrachloroethane.

The following examples are submitted for a better understanding of theinvention.

A typical copolyester prepared in accordance with this invention is asfollows. 87.3 Grams (0.45 moles) of dimethyl terephthalate, 8 grams ofdimethyl glutarate (0.05 moles), 56.64 grams of 1,6 hexanediol (0.48moles) and 55.12 (0.52 moles) of diethylene glycol, and 1 ml ofn-butanol solution of telanium tetraisopropoxide which is 1.24% telaniumare weighed with a 500 ml. single-neck round-bottom flask equipped witha nitrogen inlet, stirrer, vacuum outlet and a condensing flask. Theflask is heated at 200° C. in a metal bath for three hours with anitrogen sweep over the reaction mixture. When the theoretical amount ofmethanol has distilled from the reaction mixture the metal bathtemperature is increased to 260° C. and the pressure in the flaskreduced to 0.5 to 0.1 mm of mercury. The flask is heated at 260° C. at areduced pressure of 0.5 to 0.1 mm of mercury for 1 hr. The flask is thenremoved from the bath and allowed to cool as the polyester crystallizes.Gas chromatographic analysis of the polymer reveals the copolyestercontains the following mole percent of the reaction residues: dimethylterephthalate, 90 mole %; dimethyl glutarate, 10 mole %; 1,6 hexanediol,70 mole %; and 30 mole % diethylene glycol. The copolyester has aninherent viscosity of 0.78 and a crystalline melting point of 107° C.This copolyester is an excellent fabric adhesive.

The polyester adhesives, prepared as described above, are cryogenicallyground and screened to obtain a powder that passes a 70 mesh screen. Thepowders are applied from an engraved roll to a cotton interlining fabricto form an interlining containing rows of adhesive dots across theinterlining fabric. The interlining is used to bond two different facefabrics, wool/polyester and polyester/cotton. The interlining are bondedto fabrics by pressing 4 inch squares of interlining to 4 inch squaresof face fabric using either steam or an electric press. The bondedfabrics are laundered and dry cleaned then cut into strips 1 inch wideand T-peel strength determined using an Instron Tensile Tester beforeand after laundering and dry cleaning. The T-peel strengths are anaverage of three determinations per sample.

Examples of copolyester adhesives are shown in Table 1 in Examples 1through 7. The examples show that copolyesters based on terephthalicacid and a second dicarboxylic acid, glutaric (Examples 1 and 2), adipic(Example 3), succinic (Example 4) and isophthalic (Examples 5, 6 and 7)and a mixed glycol system which is 1,6 hexanediol and diethylene glycol,produce copolyesters which are grindable into powder, have rapidcrystallization rates, and have sufficient crystallinity, insolubilityin dry cleaning solvents and low temperature bonding characteristicswhich make them useful as fabric adhesives. Example 8 is an example of alow melting copolyester (95° C.) which has some crystallinity (ΔH_(f)-2.5 cal/g.) and has good adhesion to polyester/cotton. However, thepolymer has a slow crystallization rate from the melt and remains tackyfor 30 minutes or longer after application and suffers a considerableloss of bond strength during dry cleaning. Example 9 containsterephthalic acid, 1,6 hexanediol and diethylene glycol (without asecond acid), but will not adhere to polyester/cotton when bonded at110° C., thus it is too high melting (143° C.) to be useful as a fabricadhesive for fragile fabrics. This copolyester will bond fabric at 160°C. but this bonding temperature is not satisfactory for most fabrics.Example 10 is another example of a low melting copolyester that requirestoo high bonding temperature for most fabrics and has poor adhesion whenbonded at 110° C.

The copolyester in Example 11 has sufficient crystallinity (ΔH_(f) -5.1cal/g.) and produces sufficient bond strength (1.8 lb.) when bonded at110° C.; however, the copolyester suffers a severe loss in bond strengthduring dry cleaning. (T-peel strength is only 0.1 lb. after drycleaning). Example 12 is a copolyester ground into powder, and used tomake an interlining which is tested as a fabric adhesive after bondingto a polyester/cotton face fabric. Examples 13 and 14 are examples ofsemicrystalline low melting copolyesters which will adhere to fabricwhen bonded at 110° C. but are not useful as fabric adhesives because ofprolonged tackiness (slow crystallization rate), are very difficult togrind, and have poor resistance to dry cleaning solvents.

                                      TABLE 1                                     __________________________________________________________________________    Example No.    1         2          3                                         __________________________________________________________________________    Molar percentages of                                                                         80 terephthalic acid                                                                    85 terephthalic acid                                                                     75 terephthalic acid                      acid and glycol                                                                              20 glutaric acid                                                                        15 glutaric acid                                                                         25 adipic acid                            components     20 diethylene glycol                                                                    25 diethylene glycol                                                                     15 diethylene glycol                                     80 1,6-hexanediol                                                                       75 1,6-hexanediol                                                                        85 1,6-hexanediol                         Inherent viscosity                                                                           0.76      0.87       0.81                                      ΔH.sub.f, cal/g                                                                        5.2       4.8        5.3                                       T-Peel strength at                                                            23° C. lb/in                                                                          2.7       2.2        2.1                                       T-Peel strength after                                                                        2.6       2.1        2.0                                       dry cleaning (commercial)                                                     5 cycles lb/in                                                                Crystalline Melting point,                                                    °C.     104       106        107                                       Bonding Temperature, °C.                                                              110                                                            Type Failure   None      None       None                                      Grindability   Excellent Excellent  Excellent                                 Crystallization Half Time                                                     (Min.)         1.8       1.5        2                                         __________________________________________________________________________    Example No.    4         5          6                                         __________________________________________________________________________    Molar percentages of                                                                         80 terephthalic acid                                                                    75 terephthalic acid                                                                     85 terephthalic acid                      acid and glycol                                                                              20 succinic acid                                                                        25 isophthalic acid                                                                      15 isophthalic acid                       components in  20 diethylene glycol                                                                    15 diethylene glycol                                                                     25 diethylene glycol                      polyester      80 1,6-hexanediol                                                                       85 1,6-hexanediol                                                                        75 1,6-hexanediol                         Inherent viscosity                                                                           0.75      0.79       0.84                                      ΔH.sub.f, cal/g                                                         T-Peel strength at                                                                           1.7       1.9        2.1                                       23° C. lb/in                                                           T-Peel strength after                                                                        1.5       1.9        2.0                                       dry cleaning (5 cycles)                                                       lb/in                                                                         Crystalline Melting point,                                                    °C.     105       104        104                                       Bonding Temperature, °C.                                                              110       100        100                                       Type Failure   None      None       None                                      Grindability   Excellent Excellent  Excellent                                 Crystallization Half Time                                                     (Min.)         1         1.5        1.5                                       Coating weight, g/yd                                                                         16        22         15                                        __________________________________________________________________________    Example No.    7         8 (Control)                                                                              9 (Control)                               __________________________________________________________________________    Molar percentage of                                                                          85 terephthalic acid                                                                    70 terephthalic acid                                                                     100 terephthalic acid                     acid and glycol                                                                              15 isophthalic acid                                                                     30 isophthalic acid                                                                      90 1,6 hexanediol                         components in  35 diethylene glycol                                                                    25 azealic acid                                                                          10 diethylene glycol                      polyester      65 1,6-hexanediol                                                                       100 1,4-butanediol                                   Inherent viscosity                                                                           0.72      0.84       0.76                                      ΔH.sub.f, cal/g                                                                        4.5       2.5        8.0                                       T-Peel strength at                                                                           2.2       2.1        0.0                                       23° C. lb/in                                                           T-Peel strength after                                                                        2.1       0.8        --                                        dry cleaning (5 cycles)                                                       lb/in                                                                         Crystalline Melting point,                                                    °C.     104       95         143                                       Bonding Temperature, °C. 110                                                          Yes                  Won't Bond                                Type Failure   None      Polymer tacky 30 min.                                                                    --                                                                 and poor dry-clean                                                            resistance                                           Grindability   Excellent Poor       Excellent                                 Crystallization Half Time                                                     (Min.)         2.2       >20        <1                                        __________________________________________________________________________    Example No.    10 (Control)                                                                            11 (Control)                                                                             12                                        __________________________________________________________________________    Molar percentages of                                                                         80 terephthalic acid                                                                    65 terephthalic acid                                                                     84 terephthalic acid                      acid and glycol                                                                              20 isophthalic acid                                                                     35 1,4 cyclohexane-                                                                      16 isophthalic acid                       components in  100 1,6-hexanediol                                                                      dicarboxylic                                                                             60 1,6-hexanediol                         polyester                acid       40 1,4-butanediol                                                  100 1,6 hexanediol                                   Inherent viscosity                                                                           0.72      0.82       0.64                                      ΔH.sub.f, cal/g                                                                        6.5       5.1        3.86                                      T-Peel strength at                                                                           0.2       1.8        2.1                                       23° C. lb/in                                                           T-Peel strength after                                                                        0.2       0.1        1.9                                       dry cleaning (5 cycles)                                                       lb/in                                                                         Crystalline Melting point,                                                    °C.     130       11° C.                                                                            112                                       Bonding Temperature, °C. 110                                           Type Failure   Poor Adhesion                                                                           Poor dry cleaning                                                                        None                                      Grindabiltiy   Excellent Excellent  Excellent                                 Coating wt., g/yd.sup.2                                                                      20        18         20                                        Crystallization Half Time                                                     (Min.)         1.5       1          2                                         __________________________________________________________________________                Example No.  13 (Control)                                                                             14 (Control)                              __________________________________________________________________________                Molar percentages of                                                                       50 terephthalic acid                                                                     50 terephthalic acid                                  acid and glycol                                                                            50 adipic acid                                                                           20 isophthalic acid                                   components in                                                                              100 ethylene glycol                                                                      30 azealic acid                                       polyester               100 1,4 butanediol                                    Inherent viscosity                                                                         0.78       0.84                                                  ΔH.sub.f, cal/g                                                                      1.2        1.45                                                  T-Peel strength at                                                                         2.1        2.0                                                   23°  C. lb/in                                                          T-Peel strength after                                                                      0.4        0.3                                                   dry cleaning (5 cycles)                                                       Crystalline Melting point,                                                    °C.   110        115                                                   Bonding temperature, °C.                                                            110        110                                                   Type Failure Tacky, dry-clean                                                                         Tacky, dry-clean                                                   Failure    Failure                                               Grindability Poor       Poor                                                  Coating weight, g/yd.sup.2                                                                 21         19                                                    Crystallization Half Time,                                                    (Min.)       >20        >15                                       __________________________________________________________________________

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

I claim:
 1. A textile fabric laminated to a substrate by means of afusible interlining adhesive comprising a copolyester derived from atleast 40 mol percent terephthalic acid, about 10 to about 90 molepercent 1,6-hexanediol and about 90 to about 10 mol percent diethyleneglycol, said copolyester having a crystalline melting point of about40°-130° C., a glass transition temperature of about -10 to about 30° C.and a heat of fusion of about 1-10 calories per gram.
 2. A textilefabric laminated to a substrate by means of a fusible interliningadhesive comprising a copolyester derived from at least 40 mol percentterephthalic acid, about 10 to about 90 mol percent 1,6-hexanediol andabout 90 to about 10 mol percent diethylene glycol, said copolyesterhaving a crystalline melting point of about 80°-115° C., a glasstransition temperature of about -10° to about 30° C. and a heat offusion of at least 3.0 calories per gram.